In recent years, in an optical communication system which transmits an optical signal via an optical fiber, a speedup of a transmission of an optical signal is remarkable for responding to increase of communication traffic due to population of the Internet, where the transmission speed is being switched from 2.5 Gb/s to 10 Gb/s and research and development is being now advanced toward realization of a transmission speed of 40 Gb/s. According to such trends, it is required to meet a speeding-up regarding a transmission speed of a signal which is handled by an optical transmitting/receiving device.
The optical transmitting/receiving device converts a data signal to be transmitted from an electric signal to an optical signal to transmit the optical signal via an optical fiber for transmission, and receives an optical signal via an optical fiber for reception to reproduce the received optical signal to an electric signal.
As a light receiving element module used in such a kind of light receiver, for example, the technique described in Japanese Patent Publication No. 2907203 has been well known. In the patent publication, an optical module has been disclosed which is provided with a box-like housing which accommodates a light receiving element and has a mounting face on which the light receiving element is mounted, a sleeve which extends from a side wall of the box-like housing in a predetermined direction and supports a ferrule mounted at a distal end of an optical fiber in a state that the ferrule has been accommodated therein, an oval face reflecting mirror which is accommodated in the box-like housing for coupling the optical fiber and the light receiving element optically, and a supporting structure for holding the oval face reflecting mirror at a predetermined position inside the box-like housing in a state that the oval face reflecting mirror has been separated from the mounting face in the box-like housing by a predetermined distance.
in the technique described in the patent publication, however, since the oval face reflecting mirror is used, it is necessary to elongate a focal length of the reflecting mirror in order to arrange the optical fiber and the light receiving element optimally, which causes such a problem that the light receiving element module can not be reduced in size. Further, since a space between a reflecting point of the reflecting mirror and the light receiving element is large and the focal length is long, a thermal expansion of the material for the reflecting mirror occurs due to an environmental temperature. As a result, there is a problem that since change of an image point position becomes large, a compensation unit for the image point position illustrated in the Japanese Patent Publication No. 2907203 is required for preventing the change, which results in complication in structure. Furthermore, since the shape of the reflecting mirror has the oval face, there occurs such a problem that it is necessary to use a mirror-finishing milling machine for manufacturing a forming mold for a mirror face used in a plastic mold and it is difficult to secure a face accuracy.
Accordingly, an object of the present invention is to provide a light receiving element module with a simple structure, which does not require a complicated structure such as a temperature compensation unit for an image point position, and which can be reduced in size.